1. Field of the Invention
This invention relates to a polyolefin resin composition having highly flame retardant properties and superior heavy metal deterioration resistance, heat deterioration resistance and weather resistance and when molded, affording a molded product having an excellent appearance. More particularly it relates to a flame retardant polyolefin resin composition having a halogen-containing flame retardant, antimony trioxide, a crosslinking agent, a specified thiophosphite and if necessary, a specified processing aid, blended with a polyolefin resin, and having superior heavy metal deterioration resistance, heat deterioration resistance, weather resistance, highly flame retardant properties, and drip-preventing properties and superior processability, and when molded, affording a molded product having a superior appearance.
2. Description of the Prior Art
Since polyolefin resins are superior in processability, chemical resistance, weather resistance, electric characteristics, they have been very often used in various fields including fields of parts of domestic electric products.
On the other hand, however, the resins have drawbacks that they are very readily combustible, and when burnt, once liquefy due to thermal decomposition, and then there occur dropping of ignited droplets or non-ignited droplets and falling down of combustion pieces (hereinafter such dropping materials and falling-down materials will be referred to as "drip" and the properties of causing the drip will be referred to as "dripping properties"). The presence or absence of this drip is one of important factors at the time of evaluating flame retardant properties of the resins, and if the drip is present, their flame retardant properties are low ranked even when the self-extinguishing properties are superior. As described above, improvement in the dripping properties is one of serious problems in the art of making the resins flame retardant. Thus, for making polyolefin resins flame retardant, various proposals have so far been made.
As general processes for making the resins flame retardant, addition of an organic halogen-containing flame retardant, antimony trioxide and a salt of a higher fatty acid with a specified metal to polyolefin resins (Japanese patent publication No. Sho 51-25061/1976), addition of a nitrogen-containing compound or a hydrous inorganic compound as a flame retardant to polyolefin resins and the like processes have been carried out.
However, products obtained by merely adding an organic halogen-containing flame retardant to polyolefin resins are superior in the self-extinguishing properties at the time of combustion, but they have a drawback of causing drip at the time of combustion.
Further, products obtained by adding a hydrous inorganic compound such as magenesium hydroxide as a flame retardant to polyolefin resins are superior in the dripping properties and also have self-extinguishing properties to a certain extent, but in order to impart a highly flame retardant effectiveness, it is necessary to add a large quantity of the inorganic compound to polyolefin resins; thus polyolefin resin compositions obtained by adding a large quantity of the inorganic compound have a drawback that their molding processability deteriorates due to reduction in the fluidity of the melt and the mechanical strength of molded products obtained by molding the compositions lowers; hence the practical quantity thereof added is limited in the aspect of physical properties and it is difficult to make the resins highly flame retardant.
In order to overcome these drawbacks, a process of using a bromine-containing flame retardant and a boron-fluoride salt together with polypropylene (Japanese patent application laid-open No. Sho 54-163937/1979), a process of blending a silicon-modified ethylenea-propylene rubber and a flame retardant with a polyethylene resin, followed by crosslinking the blend with an organic peroxide (Japanese patent application laid-open No. Sho 55-110139/1980), a process of adding a silane coupling agent, an ethylene-propylene rubber, chlorinated polyethylene and a flame retardant to a polyethylene resin, followed by molding the mixture and exposing the resulting folded product to water to effect crosslinking (Japanese patent application laid-open No. Sho 55-45716/1980), and other processes have been disclosed.
Further, a flame retardant rubber composition obtained by blending an organic flame retardant, a polyfunctional compound, a cyclic compound having a specified structure, a mineral powder and an organic peroxide with an ethylene-propylene copolymer rubber has been disclosed (Japanese patent application laid-open No. Sho 56-00845/1981) has been disclosed.
The present inventors have made extensive research in order to obtain a polyolefin resin composition improves dripping properties, has highly flame retardant properties and when molded, affords a molded product having an excellent appearance, and as a result, have found that a composition obtained by blending to polyolefin resin, definite quantities of a halogen-containing flame retardant, antimony trioxide, a crosslinking agent and a specified thiophosphite or a composition further having a processing aid blended therein affords, when molded, a molded product having highly flame retardant properties, no dripping properties, a smooth surface and an excellent appearance, and superior heavy metal deterioration resistance, heat deterioration resistance and weather resistance, and have completed the present invention based on this finding.